Wind turbine blade root and process for manufacturing a wind turbine blade root

ABSTRACT

A wind turbine blade root having: an annular structure extending about a main axis and made of a composite material including a matrix and reinforcing fibers; first longitudinal reinforcing elements, which are incorporated in the annular structure, extend in the direction of the main axis, and are spaced apart in a circle about the main axis; and an annular reinforcing element connecting the first longitudinal reinforcing elements and having first coupling portions for connection to the first longitudinal reinforcing elements.

PRIORITY CLAIM

This application is a national stage application of PCT/IB2014/060142,filed on Mar. 25, 2014, which claims the benefit of and priority toItalian Patent Application No. MI2013A 000449, filed on Mar. 25, 2013,the entire contents of which are each incorporated by reference herein.

BACKGROUND

Certain wind turbines are known to comprise a tower, a nacelle, a hub,and a plurality of blades. The nacelle typically houses an electricmachine, and devices for controlling the wind turbine.

The nacelle is fitted to the tower to rotate about a substantiallyvertical axis, and supports the hub for rotation.

Each blade comprises a reinforcing beam, extending substantially thewhole length of the blade, and a shell defining an airfoil. The shell isfixed to the reinforcing beam, and is usually made of composite materialwith a resin matrix reinforced with glass or carbon fibers.

The blades in turn are fitted to the hub in rotary manner, to enableadjusting the attack (or pitch) angle.

More specifically, the blades are connected to the hub by a blade roots,which substantially serves to transmit loads between the blade and thehub. Moreover, the connection of blade root to the hub by a bearingenables adjusting the orientation and pitch angle of the blade.

The blade root is normally an annular element, and may either beintegral with the body of the blade or produced separately and joined tothe blade body. The root and the blade body are made from the samecomposite material. The blade root, however, comprises longitudinalreinforcing elements to withstand the severe loads caused by the weight(several tons) and length (tens of meters) of the blade and preventstructural damage or severe deformation. More specifically, the bladeroot has an outer annular shell and inner annular shell, both made ofcomposite material, and between which the longitudinal reinforcingelements are incorporated.

The blade root also comprises fasteners for connection to an outer metalring, which may be a bearing race or a structural element in turnconnected to the hub by a bearing.

According to one known solution, described in European Patent No EP1633624 B1, threaded bushings tapering towards their distal end (withrespect to the hub (i.e., towards the blade tip)) serve both aslongitudinal reinforcing elements and as elements for fastening to anouter metal ring for connection to the hub. The bushings are fixedindividually between the inner and outer annular shells, and areconnected to a bearing on the hub by respective studs.

Known solutions are especially critical as regards transmitting severeloads between the blade body, the reinforcing elements, and the hub.That is, stress is transmitted to the blade via the longitudinalreinforcing elements, which only interact with one another via theannular shell material. This may therefore result in severely unbalancedload distribution, especially at certain angles during rotation. In theevent of even microscopic defects, and at times even with asubstantially sound structure, forces may concentrate to such an extentas to produce or propagate damage in the composite material.

SUMMARY

The present disclosure relates to a wind turbine blade root, and to aprocess configured to manufacture a wind turbine blade root.

It is an advantage of the present disclosure to provide a wind turbineblade root, and a process configured to manufacture a wind turbine bladeroot, configured to eliminate certain of the drawbacks described and, inparticular, to improve load transmission.

According to the present disclosure, there is provided a wind turbineblade root comprising:

an annular structure extending about a main axis and made of a compositematerial including a matrix and reinforcing fibers;

first longitudinal reinforcing elements, which are incorporated in theannular structure, extend in the direction of the main axis and arespaced apart in a circle about the main axis; and

-   -   an annular reinforcing element connecting the first longitudinal        reinforcing elements and having first coupling portions        configured to couple to the first longitudinal reinforcing        elements.

The annular reinforcing element serves to strengthen the blade rootstructure and distribute stress between the longitudinal reinforcingelements, thus preventing force concentrations, so load is transmittedmore effectively between the blade body and the blade root reinforcingelements.

According to a further aspect of the disclosure, the annular reinforcingelement has threaded holes, which alternate with the first couplingportions, have respective axes parallel to the main axis and areaccessible from a proximal edge of the annular structure.

The threaded holes in the annular reinforcing element may beadvantageously exploited to insert screws required for connection to thehub. Load is thus transmitted between the blade and the hub via theannular reinforcing element, as opposed to the longitudinal reinforcingelements, which serve to transmit load between the annular reinforcingelement and the blade body. The connecting points being connected by theannular reinforcing element also assists in improving forcedistribution.

According to a further aspect of the disclosure, the blade rootcomprises second longitudinal reinforcing elements parallel to the mainaxis and arranged in a circle about the main axis, in angular positionscorresponding to respective first longitudinal reinforcing elements; andthe annular reinforcing element connects the second longitudinalreinforcing elements and comprises second coupling portions forconnection to the second longitudinal reinforcing elements.

Using a second set of longitudinal reinforcing elements increases thearea over which to transmit load to the composite-material structure. Sothe longitudinal reinforcing elements may be made smaller, while stillensuring gradual force transmission.

According to the present disclosure, there is also provided a processconfigured to manufacture a wind turbine blade root, the processcomprising:

forming a first portion of a first annular layer of composite materialabout a main axis, the composite material comprising a matrix andreinforcing fibers;

placing first longitudinal reinforcing elements in the direction of themain axis and spaced apart in a circle on the first portion of the firstannular layer; and

connecting the first longitudinal reinforcing elements by a firstportion of an annular reinforcing element having first coupling portionsconfigured to couple to the first longitudinal reinforcing elements.

Additional features and advantages are described in, and will beapparent from the following Detailed Description and the figures.

BRIEF DESCRIPTION OF THE DRAWINGS

A number of non-limiting embodiments of the present disclosure will bedescribed by way of example with reference to the attached drawings, inwhich:

FIG. 1 shows a wind turbine;

FIG. 2 shows a front view of a wind turbine blade root in accordancewith one embodiment of the present disclosure and incorporated in theFIG. 1 wind turbine;

FIG. 3 shows a lateral section, along line III-III in FIG. 2, of theFIG. 2 blade root;

FIG. 4 shows a lateral section, along line IV-IV in FIG. 2, of the FIG.2 blade root;

FIG. 5 shows a front section, along line V-V in FIG. 3, of the FIG. 2blade root;

FIG. 6 shows a front view of a wind turbine blade root in accordancewith a different embodiment of the present disclosure;

FIG. 7 shows a lateral section, along line VII-VII in FIG. 6, of theFIG. 6 blade root;

FIG. 8 shows a lateral section, along line VIII-VIII in FIG. 6, of theFIG. 6 blade root;

FIG. 9 shows a front section, along line IX-IX in FIG. 7, of the FIG. 6blade root;

FIG. 10 shows a view in perspective of a first portion of the FIG. 2blade root at an initial stage in a manufacturing process in accordancewith one embodiment of the present disclosure;

FIGS. 11 and 12 show views in perspective of the FIG. 10 blade portionat successive stages of the process;

FIG. 13 shows a view in perspective of a second portion of the FIG. 2blade root at one stage of the process;

FIGS. 14 and 15 show views in perspective of the FIG. 13 blade portionat successive stages of the process.

DETAILED DESCRIPTION

Referring now to the example embodiments of the present disclosureillustrated in FIGS. 1 to 15, number 1 in FIG. 1 indicates as a whole awind turbine. Wind turbine 1 comprises a tower 2, a nacelle 3, a hub 4,and a plurality of blades 5. Nacelle 3 houses an electric machine anddevices configured to control wind turbine 1 (which are not shown forthe sake of simplicity).

Blades 5 are fitted to hub 4, which in turn is fitted in rotary mannerto nacelle 3.

Nacelle 3 is in turn fitted to tower 2 to rotate about a substantiallyvertical axis of rotation to position blades 5 into the wind. Each blade5 can be adjusted about a respective longitudinal axis to a respectiveattack (pitch) angle with respect to the wind direction.

Each blade 5 comprises a blade root 10, to which are connected anaerodynamic shell 11 and an inner reinforcing beam (not shown in thedrawings). Blade root 10 connects blade 5 to hub 4, and transmits loadsbetween aerodynamic shell 11 and hub 4.

The blade root 10 of one of blades 5, to which reference is madehereinafter purely by way of example, is shown in more detail in FIGS.2-5.

In the embodiment shown, blade root 10 comprises an annular structure 12incorporating first longitudinal reinforcing elements 13 and secondlongitudinal reinforcing elements 14 mutually connected by a reinforcingring 15.

Annular structure 12 extends about a main axis A, and is made of acomposite material comprising a polymer matrix and reinforcing (e.g.,glass or carbon) fibers.

Annular structure 12 comprises an outer annular shell 16 and innerannular shell 17, between which first longitudinal reinforcing elements13 and second longitudinal reinforcing elements 14 are retained.

More specifically, first longitudinal reinforcing elements 13 and secondlongitudinal reinforcing elements 14 are made of metal or metal alloy(e.g., steel) and have respective substantially parallelepiped-shapedproximal ends 13 a, 14 a, and respective tapered (e.g., wedge-shaped)distal ends 13 b, 14 b.

Here and hereinafter, the terms ‘proximal’ and ‘distal’ with referenceto parts of a generic element indicate parts located, in use, on theside of the element closer to the hub rotation axis, and on the side ofthe element further from the hub rotation axis and closer to theradially outer end of the blade, respectively.

First longitudinal reinforcing elements 13 are fixed to outer annularshell 16 by a first adhesive layer 18, extend in the direction of mainaxis A, and are spaced apart in a circle about main axis A. Morespecifically, the proximal ends 13 a of first longitudinal reinforcingelements 13 are located close to a proximal edge 12 a of annularstructure 12.

Similarly, second longitudinal reinforcing elements 14 are fixed toinner annular shell 17 by a second adhesive layer 19, extend in thedirection of main axis A, and are also spaced apart in a circle, withrespective proximal ends 14 a located close to proximal edge 12 a ofannular structure 12. Moreover, second longitudinal reinforcing elements14 are located in angular positions corresponding to and radiallyinwards of respective first longitudinal reinforcing elements 13.

The proximal ends 13 a, 14 a of first longitudinal reinforcing elements13 and corresponding second longitudinal reinforcing elements 14 contactone another along respective faces. Whereas the distal ends 13 b, 14 bof first longitudinal reinforcing elements 13 and corresponding secondlongitudinal reinforcing elements 14 are separated by an intermediatelayer 20 of annular structure 12, also made of composite material.Intermediate layer 20 is clamped between first longitudinal reinforcingelements 13 and second longitudinal reinforcing elements 14 by thecomposite material setting. In an embodiment (not shown in thedrawings), however, first longitudinal reinforcing elements 13 andcorresponding second longitudinal reinforcing elements 14 are alsogripped together by screw fasteners.

Reinforcing ring 15 is made of metal or metal alloy (e.g., steel) andmay either be formed in one piece or comprise two or more ring portionsjoined to one another.

Reinforcing ring 15 connects first longitudinal reinforcing elements 13and second longitudinal reinforcing elements 14 to one another. Morespecifically, reinforcing ring 15 has first coupling portions 15 aconfigured to couple to first longitudinal reinforcing elements 13, andsecond coupling portions 15 b configured to couple to secondlongitudinal reinforcing elements 14. First coupling portions 15 a aredefined by respective longitudinal slots in an outer face of thereinforcing ring. First coupling portions 15 a extend from one side tothe other of reinforcing ring 15, between flat opposite faces thereof,in a direction parallel to main axis A, and are the same width as firstlongitudinal reinforcing elements 13. Second coupling portions 15 b aredefined by respective longitudinal slots in an inner face of reinforcingring 15, and in angular positions corresponding to respective firstcoupling portions 15 a. Like these, second coupling portions 15 b extendfrom one side to the other of reinforcing ring 15, between flat oppositefaces thereof, in a direction parallel to main axis A, and are the samewidth as second longitudinal reinforcing elements 14.

First longitudinal reinforcing elements 13 and second longitudinalreinforcing elements 14 have respective first transverse slots 13 c andsecond transverse slots 14 c, in intermediate portions betweenrespective proximal ends 13 a, 14 a and distal ends 13 b, 14 b. Firsttransverse slots 13 c and second transverse slots 14 c are of a widthequal to the thickness of reinforcing ring 15, and have profilesmatching up with first coupling portions 15 a and second couplingportions 15 b respectively.

Reinforcing ring 15 is joint-connected to first longitudinal reinforcingelements 13 and second longitudinal reinforcing elements 14.

Reinforcing ring 15 also has threaded holes 23 alternating with firstcoupling portions 15 a and second coupling portions 15 b, and havingrespective axes F parallel to main axis A. In other words, the portionsof reinforcing ring 15 in which threaded holes 23 are formed are locatedin gaps between circumferentially pairs of adjacent first longitudinalreinforcing elements 13 and second longitudinal reinforcing elements 14.

The distal ends 13 b, 14 b of first longitudinal reinforcing elements 13and second longitudinal reinforcing elements 14 are separatedcircumferentially by fillers 25 (e.g., foam material). An outer spacerring 27 and inner spacer ring 28, also made of foam material, arelocated radially between intermediate layer 20 and outer annular shell16, and between intermediate layer 20 and inner annular shell 17,respectively. Outer spacer ring 27 and inner spacer ring 28 extendaxially between the distal ends 13 b, 14 b of first longitudinalreinforcing elements 13 and second longitudinal reinforcing elements 14and a distal edge 12 b of annular structure 12.

Spacers 30 with holes are located between the proximal ends 13 a, 14 aof first longitudinal reinforcing elements 13 and second longitudinalreinforcing elements 14, and extend axially between the proximal edge 12a of annular structure 12 and reinforcing ring 15. The holes enable forinserting studs 31 inside respective threaded holes 23 to fix blade root10 to a race of a bearing 32 (indicated by the dash-and-dot line inFIGS. 3 and 4) for connection to hub 4 of wind turbine 1.

The structure of blade root 10—with reinforcing ring 15 with threadedholes 23 for connection to the hub, and which connects all oflongitudinal reinforcing elements 13, 14 to one another—provides forsafely, or at least relatively more safely, transmitting loads betweenhub 4 and each blade 5. It should be appreciated that the elements firstinvolved are reinforcing ring 15 on the blade 5 side, and the studs onthe hub 4 side. Reinforcing ring 15 aids in strengthening the blade rootstructure and in distributing load more evenly by also exploiting theconnection to longitudinal reinforcing elements 13, 14.

Moreover, longitudinal reinforcing elements 13, 14, being arranged intwo sets, may advantageously be made smaller.

It should be appreciated that providing two sets of longitudinalreinforcing elements, however, is not essential.

In the FIG. 6-9 embodiment, a blade root 110 of a wind turbine blade(neither shown as a whole) comprises an annular structure 112incorporating longitudinal reinforcing elements 113 connected to oneanother by a reinforcing ring 115.

Annular structure 112 extends about a main axis A′, and is made of acomposite material comprising a polymer matrix and reinforcing (e.g.,glass or carbon) fibers.

Annular structure 112 comprises an outer annular shell 116 and innerannular shell 117, between which longitudinal reinforcing elements 113are retained.

Longitudinal reinforcing elements 113 are made of metal or metal alloy(e.g., steel) and have respective parallelepiped-shaped proximal ends113 a, and respective tapered (e.g., wedge-shaped) distal ends 113 b.

Longitudinal reinforcing elements 113 are fixed to outer annular shell116 by a first adhesive layer 118 and to inner annular shell 117 by asecond adhesive layer 119, extend in the direction of main axis A′, andare spaced apart in a circle about main axis A′. More specifically, theproximal ends 113 a of longitudinal reinforcing elements 113 are locatedclose to a proximal edge 112 a of annular structure 112.

Reinforcing ring 115, which is made of metal or metal alloy (e.g.,steel) connects longitudinal reinforcing elements 113 to one another.More specifically, reinforcing ring 115 has coupling portions 115 adefined by respective longitudinal slots in an outer face of thereinforcing ring. Coupling portions 115 a extend from one side to theother of reinforcing ring 115, between flat opposite faces thereof, in adirection parallel to main axis A′, and are the same width aslongitudinal reinforcing elements 113.

Longitudinal reinforcing elements 113 have respective transverse slots113 c in intermediate portions between respective proximal ends 113 aand distal ends 113 b. Transverse slots 113 c are of a width equal tothe thickness of reinforcing ring 115, and have profiles matching upwith respective coupling portions 115 a.

Coupling between reinforcing ring 115 and longitudinal reinforcingelements 113 is obtained by shape or joint.

Reinforcing ring 115 also has threaded holes 123 alternating withcoupling portions 115 a and having respective axes F′ parallel to mainaxis A′. In other words, the portions of reinforcing ring 115 in whichthreaded holes 123 are formed are located in gaps betweencircumferentially adjacent longitudinal reinforcing elements 113.

The distal ends 113 b of longitudinal reinforcing elements 113 areseparated circumferentially by fillers 125 (e.g., foam material). Aspacer ring 127, also made of foam material, is located radially betweenouter annular shell 116 and inner annular shell 117, and extends axiallybetween the distal ends 113 b of longitudinal reinforcing elements 113and a distal edge 112 b of annular structure 112.

Spacers 130 with holes are located between the proximal ends 113 a oflongitudinal reinforcing elements 113, and extend axially between theproximal edge 112 a of annular structure 112 and reinforcing ring 115.The holes enable for inserting studs 131 inside respective threadedholes 123 to fix blade root 110 to a race of a bearing 132 (indicated bythe dash-and-dot line in FIGS. 7 and 8) for connection to a wind turbinehub.

FIGS. 10-14 show a process configured to manufacture the blade root 10in FIGS. 2-5. In one embodiment of the disclosure, blade root 10 isproduced separately in two substantially identical halves which areultimately joined together. In what follows, the process will bedescription in detail in relation to only one of the two halves and willbe briefly summarized for the other half. It is understood, however,that what is described and illustrated also applies, with no majordifferences, to both halves of blade root 10.

Firstly (FIG. 10), prepreg sheets (i.e., sheets of composite materialwith fibers preimpregnated with partly polymerized resin) areconformably placed inside a semicylindrical female mold (not shown inthe drawings) to form a first outer half-shell 16′ eventually formingpart of outer annular shell 16. In the following description, referenceis consistently made to the use of prepreg sheets, this should in no waybe inferred as limiting, in that the same result may be achieved bylaying layers of non-impregnated reinforcing fibers, and then infusingresin to form the composite material matrix.

A first adhesive layer 18′ is laminated onto first outer half-shell 16′.And a first set of first longitudinal reinforcing elements 13 is thenplaced on first adhesive layer 18′ to fix them to first outer half-shell16′. More specifically, first longitudinal reinforcing elements 13 arelaid in the direction of main axis A and spaced apart in a circle onfirst outer half-shell 16′.

As shown in FIG. 11, a first reinforcing half-ring 15′, ultimatelyforming part of reinforcing ring 15, is placed so that first couplingportions 15 a engage respective first transverse slots 13 c in firstlongitudinal reinforcing elements 13 (see also FIG. 5), firstreinforcing half-ring 15′ thus connects first longitudinal reinforcingelements 13, and the threaded holes 23 in first reinforcing half-ring15′ are located in the gaps between adjacent first longitudinalreinforcing elements 13.

Next, fillers 25 (not shown here—see FIGS. 3 and 4) are inserted betweenthe distal ends 13 b of adjacent first longitudinal reinforcing elements13, and a first outer half-spacer-ring is inserted between firstlongitudinal reinforcing elements 13 and the distal edge of first outerhalf-shell 16′ to form an even, seamless surface.

After a layer of adhesive (not shown for the sake of simplicity) islaminated on, prepreg sheets are conformably deposited to form a firstportion 20′ of intermediate layer 20. The first portion 20′ ofintermediate layer 20 extends between first reinforcing half-ring 15′and the distal edge of first outer half-shell 16′.

Another adhesive layer (not shown in the drawings) is laminated ontofirst portion 20′ of intermediate layer 20, and a first set of secondlongitudinal reinforcing elements 14 is fixed to first portion 20′. Morespecifically, second longitudinal reinforcing elements 14 are placed inangular positions corresponding to respective first longitudinalreinforcing elements 13, and so that second coupling portions 15 b offirst reinforcing half-ring 15′ engage respective second transverseslots 14 c (see also FIG. 5).

Further fillers 25, spacers 30 with holes, and a first innerhalf-spacer-ring (not shown in the drawings) are then positioned to forman even, seamless surface.

Further prepreg sheets are then deposited to form a first innerhalf-shell 17′ and so complete the first half of blade root 10 (FIG.12).

The second half is made in exactly the same way, by:

forming a second outer half-shell 16″ (FIG. 13);

laying a second set of first longitudinal reinforcing elements 13 onsecond outer half-shell 16″;

connecting the first longitudinal reinforcing elements 13 with a secondreinforcing half-ring 15″ (FIGS. 14 and 5);

assembling a second inner half-spacer-ring and further fillers 25 (notshown in the drawings);

1-23. (canceled)
 24. A wind turbine blade root comprising: an annularstructure extending about a main axis, said annular structure being madeof a composite material including a matrix and a plurality ofreinforcing fibers; a plurality of first longitudinal reinforcingelements incorporated in the annular structure, said plurality of firstlongitudinal reinforcing elements extending in a direction of the mainaxis and being spaced apart about the main axis; and an annularreinforcing element connecting the plurality of first longitudinalreinforcing elements, said annular reinforcing element having aplurality of first coupling portions configured to couple to theplurality of first longitudinal reinforcing elements.
 25. The windturbine blade root of claim 24, wherein the annular reinforcing elementhas a plurality of threaded holes, which: (i) alternate with theplurality of first coupling portions, (ii) have respective axes parallelto the main axis, and (iii) are accessible from a proximal edge of theannular structure.
 26. The wind turbine blade root of claim 24, whereinthe annular structure includes: a first annular shell, and a firstadhesive layer between the first annular shell and the plurality offirst longitudinal reinforcing elements.
 27. The wind turbine blade rootof claim 26, which includes a plurality of second longitudinalreinforcing elements extending in the direction of the main axis, saidplurality of second longitudinal reinforcing elements being arrangedabout the main axis in a plurality of angular positions respectivelycorresponding to the plurality of first longitudinal reinforcingelements, wherein the annular reinforcing element connects the pluralityof second longitudinal reinforcing elements and includes a plurality ofsecond coupling portions for connection to the plurality of secondlongitudinal reinforcing elements.
 28. The wind turbine blade root ofclaim 27, wherein the annular structure includes: a second annularshell, and a second adhesive layer between the second annular shell andthe plurality of second longitudinal reinforcing elements.
 29. The windturbine blade root of claim 27, wherein: the plurality of secondcoupling portions define a plurality of second longitudinal slots of asize corresponding to a transverse dimension of the plurality of secondlongitudinal reinforcing elements, and the plurality of secondlongitudinal reinforcing elements define a plurality of secondtransverse slots which respectively receive the plurality of secondcoupling portions of the annular reinforcing element.
 30. The windturbine blade root of claim 27, wherein each of the plurality of secondlongitudinal reinforcing elements has a tapered distal end.
 31. The windturbine blade root of claim 27, wherein the plurality of second couplingportions are arranged in angular positions respectively corresponding tothe plurality of first coupling portions.
 32. The wind turbine bladeroot of claim 31, wherein the plurality of first coupling portions andthe plurality of second coupling portions are located on respectiveradially opposite faces of the annular reinforcing element.
 33. The windturbine blade root of claim 27, wherein an intermediate layer of thecomposite material is clamped between the plurality of firstlongitudinal reinforcing elements and the plurality of secondlongitudinal reinforcing elements.
 34. The wind turbine blade root ofclaim 27, wherein the plurality of second longitudinal reinforcingelements are arranged in a circle about the main axis.
 35. The windturbine blade root of claim 24, wherein: the plurality of first couplingportions define a plurality of first longitudinal slots of a widthcorresponding to a transverse dimension of the plurality of firstlongitudinal reinforcing elements; and the plurality of firstlongitudinal reinforcing elements define a plurality of first transverseslots which respectively receive the plurality of first couplingportions of the annular reinforcing element.
 36. The wind turbine bladeroot of claim 24, wherein each of the first longitudinal reinforcingelements has a tapered distal end.
 37. The wind turbine blade root ofclaim 24, wherein the annular reinforcing element includes at least afirst annular portion and a second annular portion joined to each other.38. The wind turbine blade root of claim 24, wherein said plurality offirst longitudinal reinforcing elements are spaced apart in a circleabout the main axis.
 39. A wind turbine blade comprising: a shell; and awind turbine blade root including: an annular structure extending abouta main axis, said annular structure being made of a composite materialincluding a matrix and a plurality of reinforcing fibers; a plurality offirst longitudinal reinforcing elements incorporated in the annularstructure, said plurality of first longitudinal reinforcing elementsextending in a direction of the main axis and being spaced apart aboutthe main axis; and an annular reinforcing element connecting theplurality of first longitudinal reinforcing elements, said annularreinforcing element having a plurality of first coupling portionscoupled to the plurality of first longitudinal reinforcing elements. 40.A wind turbine comprising: a tower; a nacelle rotatable with respect tothe tower; a hub rotatable with respect to the nacelle; and at least oneblade fitted to the hub, said at least one blade including: a windturbine blade root including: an annular structure extending about amain axis, said annular structure being made of a composite materialincluding a matrix and a plurality of reinforcing fibers; a plurality offirst longitudinal reinforcing elements incorporated in the annularstructure, said plurality of first longitudinal reinforcing elementsextending in a direction of the main axis and being spaced apart aboutthe main axis; and an annular reinforcing element connecting theplurality of first longitudinal reinforcing elements, said annularreinforcing element having a plurality of first coupling portionscoupled to the plurality of first longitudinal reinforcing elements. 41.A process of manufacturing a wind turbine blade root, the processcomprising: forming a first portion of a first annular layer of acomposite material about a main axis, the composite material including amatrix and a plurality of reinforcing fibers; placing a plurality offirst longitudinal reinforcing elements in a direction of the main axis,said plurality of first longitudinal reinforcing elements being spacedapart on the first portion of the first annular layer; and connectingthe plurality of first longitudinal reinforcing elements by a firstportion of an annular reinforcing element having a plurality of firstcoupling portions to couple with the plurality of first longitudinalreinforcing elements.
 42. The process of claim 41, wherein the annularreinforcing element has a plurality of threaded holes which: (i)alternate with the plurality of first coupling portions, (ii) have aplurality of axes respectively parallel to the main axis, and (iii) areaccessible from a proximal edge.
 43. The process of claim 42, whichincludes placing a plurality of second longitudinal reinforcing elementsin angular positions corresponding to the plurality of firstlongitudinal reinforcing elements, wherein the first portion of theannular reinforcing element includes a plurality of second couplingportions in angular positions respectively corresponding to theplurality of first coupling portions on a radially opposite face. 44.The process of claim 43, which includes: placing an intermediate layerof the composite material on the plurality of first longitudinalreinforcing elements, and placing the plurality of second longitudinalreinforcing elements on the intermediate layer of the compositematerial.
 45. The process of claim 43, which includes forming a firstportion of a second annular layer of the composite material about themain axis such that the plurality of first longitudinal reinforcingelements are incorporated between the first portion of the first annularlayer and the first portion of the second annular layer to form a firstportion of an annular structure.
 46. The process of claim 45, whichincludes: forming a second portion of the first annular layer; placinganother plurality of first longitudinal reinforcing elements in thedirection of the main axis and spaced apart on the second portion of thefirst annular layer; connecting the other plurality of firstlongitudinal reinforcing elements by a second portion of the annularreinforcing element; forming a second portion of the second annularlayer of the composite material about the main axis such that the otherplurality of first longitudinal reinforcing elements are incorporatedbetween the second portion of the first annular layer and the secondportion of the second annular layer resulting in a second portion of theannular structure, symmetrical with the first portion of the annularstructure; and joining the first portion of the annular structure andthe second portion of the annular structure.
 47. The process of claim46, which includes placing another plurality of second longitudinalreinforcing elements in angular positions respectively corresponding tothe other plurality of first longitudinal reinforcing elements.
 48. Theprocess of claim 46, which includes fitting the annular structure to awind turbine hub by screws inserted inside the threaded holes.
 49. Theprocess of claim 41 wherein said plurality of first longitudinalreinforcing elements are spaced apart in a circle on the first portionof the first annular layer.